BACKGROUND: Uvulopalatopharyngoplasty(UPPP) has become the most common surgical treatment for obstructive sleep apnea syndrome(OSAS). However, the results of this therapeutic modality have been quite variable with successful results by several authors and poor results by others. Until recently, in Korea, there is only a few reports about the clinical efficacy of UPPP. A prospective study was undertaken to evaluate the effectiveness and complications of UPPP. METHODS: Twenty-six OSAS patients who had undergone UPPP with preoperative and postoperative polysomnographic studies were included in this study. Two definitions of surgical success were used. The responder was defined, using a conventional criteria, as a 50% or more reduction in apnea index(AI) or apnea-hypopnea index(AHI) after UPPP, or a postoperative Al of <10 or AHI of <20. The initial cure was defined, using our own criteria, as a postoperative Al of <5 or AHI of <10. Complications were categorized in two groups early(disorders during the first 10 postoperative days) and late. RESULTS: Eighteen patients(69.2%) were responders, and ten patients(38.5%) were considered as initial cure. On the other hand, in five patients(19.2%), postoperative polysomnographic data demonstrated deterioration compared with preoperative data. Reduction rate of Al or AHI following UPPP was not significantly related to the preoperative body mass index, Al or AHI. There was no significant change of sleep architecture before and after UPPP in responder and initial cure groups. Early complications such as pain, dyspnea, bleeding, nasal reflux, dysphagia or wound disruption were observed in all patients. Late complications such as nasal reflux, voice change, dysphagia, loss of taste, pharyngeal dryness or foreign body sensation were discovered in 22 patients(84.6%). However, all early and late complications were of minor importance. CONCLUISON: The response to UPPP was favorable in approximately 70% of OSAS patients. However, the initial cure rate of UPPP was relatively low. We suggest that selection of more appropriate surgical candidates and adequate surgical protocol is necessary to obtain a more successful result with UPPP.